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209 Cards in this Set
- Front
- Back
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What is the purpose of a desk study? |
To determine the nature, past use, and condition of the site. To determine whether this has any implications for the proposed building and its foundations |
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What is the purpose of a walk over survey? |
To confirm desk study or further investigation Identify potential hazards collect photographic evidence make detailed drawings
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What is the purpose of ground investigations? |
To determine nature and thickness of soil nature, thickness and stratum of subsoil assess allowable bearing pressure groundwater levels existing structures |
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How deep do trial pits usually go for low rise housing? |
4-5 metres. |
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Where should trial pits be positioned? |
Near the proposed foundations but not too close so it affects the actual construction |
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What is the diameter of the steel rods used to reinforce concrete? |
20-30mm |
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When were legislations for concrete foundations first introduced? |
Late 19th Century |
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Usually, how wide are strip foundations? |
500-700mm |
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What is the minimum depth for strip foundations? |
1000mm |
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When is strip foundation not acceptable? |
Large trees are present Weak or unstable soils Where strip foundations would have to be very deep to reach firm ground |
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How many piles are used to support a house? |
10-20 |
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Why is piling becoming more common? |
Increased pressure to build on brownfield sites Increased cost of carting away and tipping Easy availability of smaller piling rigs Greater understanding of piling |
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When were raft foundations common? |
1940s-1950s |
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When are raft foundations used? |
low, load bearing capacity pad or strip foundations would cover over 50% Differential movements are expected subsidence due to mining is a possibility
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What is the purpose of a site investigation? |
To ensure ground conditions are assessed and potential hazards are identified before detailed designs begin. |
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What are the key stages of a site instigation? |
Desk study Walk-over survey Ground investigation |
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What is concrete? |
A mixture of cement water and aggregates. |
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What is the difference between trenchfil foundation and traditional strip foundation |
There is a difference in thickness, Trench fill foundations use more concrete but less brick and block work. |
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When is a wide strip foundation required? |
When the bearing load capacity of the soil requires the loads to be spread over a large area. |
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In what situations are strip foundations not suitable? |
* where large trees are present in clay soils
* where trees in clay soils have recently been removed * in very weak or unstable soils * where strip foundations would have to be very deep to reach firm ground * where subsidence is likely (ie in mining areas) |
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What is the difference between displacement and replacement piling? |
A displacement pile pushes the ground out of the way as the pile is driven into the ground. In a replacement pile the ground is removed first, usually with an auger or boring machin |
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What is the function of the ground beam which sits on top of the piles? |
The ground beam ensures that the loads form the walls are transferred into the piles |
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When are rafts sometimes used? |
* Where the soil has low load bearing capacity and varying compressibility. This might include, loose sand, soft clays, fill, and alluvial soils (soils comprising particles suspended in water and deposited over a flood plain or river bed).
* Where pad or strip foundations would cover more than 50% of the ground area below the building. * Where differential movements are expected. |
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What the usual thickness of traditional strip foundation? |
150mm |
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Which type of flooring is most common for ground floors today? |
Concrete ground floors |
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Name a typical floor from the 1960's to 1980's |
Hardcore base, polythene damp proof membrane, an in situ concrete slab, floor screed |
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Where is the damp proof membrane situated? |
Either above or below the concrete slab. |
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What is the purpose of DPM? |
to isolate the slab from aggressive chemicals in the ground |
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What is the best form of DPM |
Liquid forms of DPM give the best protection |
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What is the purpose of the Hardcore? |
It fills and levels the sub floor void, prevents capillary action and provides a level base for concrete |
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Usually, how thick is the concrete slab? |
100mm thick |
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How is the concrete finished? |
With a sand/cement screed, 50mm thick. |
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Name a disadvantage of floating floors |
They can be ruined by a washing machine leak as they are made of chipboard. |
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In the last 20 years how have floors improved? |
Improvements have been made to their thermal insulation |
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Why is a thicker layer of screed needed is it is laid over insulation? |
To prevent cracking |
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In floors where does the most heat loss occur? |
Around the edges. |
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When are concrete ground bearing slabs not suitable? |
Where there aggressive chemicals in the ground Where the wage table is high On sloping ground Where the hardcore is likely to be more than 600mm thick. |
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Why are air vents needed in suspended floors? |
To circulate the air to prevent damp and condensation. |
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Why were sleeper walls honey combed? |
To allow air to circulate easily, to prevent damp and condensation |
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What are sleeper walls? |
walls situated half span of the building to support the floor joists and minimise joist depths. |
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How can joists be supported now? |
Sleeper walls or joist hangers. |
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What is the thickness of an over site on a suspended floor. |
100mm concrete or 50mm concrete onto of DPM |
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Where is Insulation situated in floors? |
Above or between joists. |
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Name five main differences to timber flooring now and 70 years ago. |
Joists are likely to span across the whole room. Joists will be supported on hangers Timber is treated against rot and insect attack Ventilation is more onerous most floors are finished with chipboard |
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What is the function of DPM, where can it be positioned, how can it be protected? |
its function is to prevent rising damp in the floor structure A sheet DPM can be laid below or above the slab, a liquid DPM can only be laid above the slab. DPMs above the slab are protected by the floor screed. You can also protect them by layering them with sand binding |
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What is the function of a floor screed and what determines its thickness |
he floor screed is designed to provide a level smooth surface thickness is largely determined by its support and the availability of any bond with the slab. |
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Describe a typical construction of a floating floor |
A concrete slab laid on a DPM Insulation boards laid on the slab acting as the resilient layer A polythene vapour check to prevent moisture in the slab affecting the chipboard. Chipboard laid with glued joints (with a 10mm gap around the perimeter for expansion) |
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Where can insulation be positioned in the ground bearing floor with screed finish? |
Between the slab and the screed. Below the slab but above the DPM Below the DPM (If the insulation board is of the right quality) |
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When is ground bearing slab not suitable? |
Solid floors
What is the function of a DPM and where can it be positioned? How can it be protected? A sheet DPM can be laid below or above the slab, a liquid DPM can only be laid above the slab. Its function is to prevent rising damp in the floor structure (through capillary action). Polythene DPMs are protected by laying them on a layer of sand blinding. This minimise the risk of puncture during the concreting process. DPMs above the slab are protected by the floor screed.
What is the function of a floor screed and what determines its thickness? The floor screed is designed to provide a level smooth surface suitable for carpets, tiling etc. Its thickness is largely determined by its support and the availability of any bond with the slab. So for example, a screed laid on a concrete slab could be 38mm. If the screed is laid on a DPM it will usually have to be thicker, say 50mm. If laid on insulation boards it may have to be 75mm thick - and reinforced with a fine gauge wire.
Describe typical construction of a floating chipboard floor (including slab etc) Typical construction includes: * where there are aggressive chemicals in the ground * where water tables are high * on sloping ground where uneven depth of hardcore may lead to differential settlement on ground likely to heave * where the hardcore is likely to be more than 600mm thick |
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Briefly describe the construction of a pre-cast concree floor |
pre-cast concrete beams spanning from load bearing wall to loadbearing wall. Concrete blocks fill the gaps in between the beams. |
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Whatimrovements were made to raised timber floors in the late 1920s and 1930s |
joist ends sat on a sleeper wall and did not touch the external load bearing wall. leeper walls were honey-combed |
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How do modern timber floors differ from those built 70 years or so ago? |
* joists are likely to span across an whole room – no sleeper walls are usually required nowadays. |
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What are upper floors made of? |
They consist of joists separated at equally distances covered with florboarding. |
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What is the purpose of a ceiling and what are the made out of nowadays? |
To hide the floor structure and to provide sound insulation, fire resistance they are usually made out of plasterboard. |
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What is the distance between two joists? |
400mm |
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What resists the joists tendency to bend? |
The joists depth |
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What resists the tendency to twist? |
The joists depth |
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How are joists supported? |
By external walls and internal loading bearing walls. |
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How has damp penetration been improved? |
The joists are only built into internal leaf of cavity walls or supported on joist hangers. Corbels also use to be used. |
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What is the purpose of battens? |
They are a temporary measure to keep the joists upright |
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Why is strutting required? |
To prevent twisting and cracking the ceiling below. |
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How can joist twisting be caused? |
By loading or by shrinkage |
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How do timber blocking or timber wedges improve flooring? |
They tighten up the fort and help minimise movement. |
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What date did the building regulations bring in the following regulation: Joists must be tied to the walls at regular intervals? |
1965 |
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What is the maximum distance between strappings of floor joists? |
2m |
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When is additional resistant required in flooring? |
When the joists are supported my joist hangers only. |
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When are trimmer joists used? |
When there is an opening in the floor i.e. for stairs. |
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Why are trimmer joists thicker? |
To cope with the increased load. |
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What is used to join trimmer joists together? |
Timber galvanised hangers |
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In the Georgian and Victorian periods what were used for floor coverings? |
Square edged boards |
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When did chipboard become the most common material for floor coverings? |
1970 |
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What are notches? |
holes in joists for pipes to run through. |
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What are holes? |
Holes are holes in joists for cables to run through. |
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Where are notches situated? |
top of the joists. |
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Where are holes situated? |
Along the central axis of the joists. |
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When a joist is built into an interleaf, how is damp penetration prevented? |
The joint between joist and block is sealed with mastic |
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What is the maximum extension of joists over walls |
100mm to prevent the cantilever affect. |
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Why do floors now include insulation? |
To prevent the transference of air born sounds and improve thermal insulation |
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Why are metal web joists now being used? |
Because notches and holes are no longer needed for services therefore the joist strength is not affected. |
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Why is concrete flooring useful? |
It produces higher levels of fire protection and can span longer than timber floors. |
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How is the opening for a modern timber floror? |
An opening is formed by trimming the joists |
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How were early ceilings forms |
Early ceilings were formed from long strips of fir nailed to the soffit of the joists and plastered with three coats of lime plaster. |
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In modern construction how are joists supported? |
Joists can be supported by building them into the blockwork inner leaf or by providing joist hangers. |
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What is the function of strutting and strapping and how is it provided? |
Strutting stops the floor joists twisting Strapping is required to provide restraint for external walls |
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How does early 20th century floor boarding differ from modern boarding? |
Modern floor boards are tongued and grooved, chipboard and other sheet material are also tongued and grooved 100 years ago most floorboards were square edged. |
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What factors affect the size of floor joss and how can the size be determined? |
their span, load, centres (spacing) and the strength of the timber. Size can be determined from tables in the Building Regulations. |
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What are the advantages of modern concrete upper floors and were are they normally used? |
high loads and are good at reducing airborne sound and providing good fire protection. |
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Where should holes and notches be provided in timber floors.? |
Notches should occur in the top of the joist, holes along the centre axis |
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What is the minimum angle concrete tiles can be laid at? |
25 degrees |
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Why are high patches more effective? |
They reduce the risk of rainwater being blown put the tiles and reduce the risk of capillary action |
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What angle are traditional tiles usually laid at? |
45 degrees |
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When are lean-to-roofs suitable? |
for small spans. typically used for rear extensions. |
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What are rafters? |
Sloping timbers in trusses |
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What are cut roofs? |
trusses with inclining pairs of rafters. |
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When were cut roofs most popular? |
Before 1960's |
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How are rafters supported to prevent them from spreading outwards? |
The feet of each rafter is tied together with a ceiling joist. (bottom of truss) |
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What is the purpose of a ridge? |
To make it easier to build the roof on site and to distribute the wind loading. |
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What is the typical rafter size? |
1000r 125 by 50mm |
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How are cavities closed? |
With a brick or block |
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Why are cavities closed? |
To prevent air or fire from the void entering the roof |
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where is the wall plate placed? |
On the inner leaf of a cavity wall bedded in mortar. |
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What is the purpose of fascia boards |
The hide the frets of the rafters and support the guttering |
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What are used to prevent the roof from lifting in high winds? |
galvanised straps are strapped to the wall plate |
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When are soffit boards required> |
When the roof overhangs the wall to hide the timbers from underneath. |
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What is the purpose of a good overhang? |
To protect the wall underneath from saturation |
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What are resistant straps used of a on roofs? |
To stabilise and restrain the gable ends. Usually 2 or 3 straps are used on each slope. |
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What is a disadvantage of closed couple roofs? |
They are only capable of limited spans as they would begin to sag and deform. |
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What are purlins? |
A purlin supports the rafters mid span. |
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When were purlin roofs most commonly found? |
before the 1960's |
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What is the typical size of a purlin? |
50to75mm wide, 200mm deep |
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What is the purpose of struts in roofs? |
To prevent the purlins from sagging under load |
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How are the struts supported? |
they sit of internal loading bearing walls |
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What are ties/collars used for? |
To prevent deformation in high winds. |
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In what period did most houses have purlins and struts in their roofs? |
1920s-1930s |
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What is the function of a wall plate and why should it be strapped down to the walls? |
A wall plate provides a fixing for the rafter feet and spreads the rafter loads across the wall |
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What is the function of ceiling joists? |
Ceiling joists provide a fixing for the plasterboard ceiling and prevent the rafters feet from spreading. |
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What is a soffit board? |
A soffit board fills the gap between fascia board and wall. |
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Why should gables be strapped to the roof structure? |
to provide restraint for the gable wall. |
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What is the function of a purlin? |
The purlin supports the rafters mid span. |
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How can purlins be supported in large roofs? |
By struts which are supported by internal walls |
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What is the most common form of roof structure today? |
Trussed rafters |
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what are the characteristics of trussed rafters? |
To be light and strong |
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How are trussed rafters held together? |
With nail plates |
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How are trusses joined to wall plates |
With special truss clips |
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What is the usual distance between each trussed rafter? |
600mm |
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What is the typical distance between cut roofs? |
400mm |
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Why are additional braces used in trussed rafter structures? |
To make the roof rigid and so that is acts as one structure |
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What is the purpose of binders? |
They maintain the distance between the trusses |
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What is the purpose of diagonal braces? |
To keep the structure rigid and to prevent lateral deformation |
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What are the advantages of trussed rafters? |
* they are cheaper and lighter
* they do not require skilled labour * they do not require internal loadbearing walls * they are fast to erect * they can be designed to very shallow pitches to suit modern roof coverings |
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How are truss members fixed together |
By metal toothed connector plates |
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How are the trusses fixed in position? |
Trusses are fixed in position by special truss clips nailed to the wall plate |
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What is the function of the bracing and binding? |
The longitudinal binders ensure the trusses stay at the correct centres and ties them all together. The diagonal brace provides triangulation and ensures that the structure remains rigid and the trusses vertical. |
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Name some disadvantages of thatch roofs? |
High fire risk and can be attacked by vermin |
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What are eaves? |
The bottom of the roof |
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What is the purpose of roofing felt? |
To provide a barrier to minimise wind load and to prevent wind and rain from entering the roof space. |
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How the felt held into place? |
With tile battens |
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How should the felt be laid at the eaves? |
Th felt should overlap and run into the gutter |
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Why should the felt be saggy? |
To allow water to drain underneath battens |
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What is a typical size for a tile batten? |
38x25mm or 50x25mm |
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How much do modern interlocking tiles overlap? |
50-75mm |
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Why do we nail of clip tiles? |
To prevent movement |
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What are ridge tiles? |
Half round tiles that are placed on the top of roofs |
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How is a valley formed? |
By two roofs joining together |
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How are hips formed? |
When roofs meet at external angles |
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Why do roofs need to be ventilated? |
To prevent condensation in roof voids |
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How is ventilation provided in roofs. |
Vents are provided at the eaves level, either side of the roof. |
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How should plain tiles be laid |
They should double lap |
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Why is slate a good material for roofing? |
It is non combustible, impermeable to water, highly resistant to frost attack and chemical attack |
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When are flashings required? |
When a roof abuts a wall or chimney |
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Name the two components of flashings |
Soakers and stepped cover flashing |
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What is a pan tile and what is a double roman? |
pantile is a single lap tile which originated in Holland. It is shaped like a rotated and flattened ‘S’. A double roman is also a single lap tile |
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What is the function of roofing felt and how should it be fixed? |
on according to the British Standard is to reduce the wind loading on roofs. It is also helpful in preventing dust and wind blown snow from getting into the roof space. |
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Explain the difference between single and double lap coverings |
single lap tile laps the one below. A double lap tile laps not just the one, below but the one below that as well. |
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How can interlocking tile roofs be finished at the verge |
use of special verge tiles or by providing an undercloak and bedding cut tiles in mortar. |
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What is a soaker? |
soaker is a small piece of lead, copper or zinc, which fits in between tiles |
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Define Headlap |
headlap is the amount by which a tile overlaps the one below it. |
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Define Gauge |
The gauge is the distance from the centre line of one batten to the centre line of the next. |
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Define Margin |
the margin is the length of tile ‘exposed’ - its distance is the same as the gauge. |
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What are the two basic functions of a wall? |
To support the loads of suspended floors and roof To provide environmental protection |
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Name the three classification of bricks |
Commmon bricks Facing bricks Engineering bricks |
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Why has clockwork become so popular? |
Because of its cost advantages over brickwork |
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What are blocks made of? |
Cement and aggregate |
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Why are dense blocks unsuitable for cavity walls? |
Because they are good conductors of heat |
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What is an advantage of dense blocks? |
They provide god sound insulation |
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Name a disadvantage of lightweight blocks |
They can be porous |
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What is the purpose of mortar? |
to bind the bricks and block together and to distribute the load through the wall |
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What improves a mortars capability of thermal and moisture movement? |
Lime |
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Why may strong mortars result in damp penetration? |
Because they are brittle and crack easily and cannot accommodate for thermal/moisture movement |
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What is pointing? |
Raking out joints and filling them with fresh mortar. |
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What is the minimum thickness of a wall? |
215mm or 1B |
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What is a header? |
A brick that joins the two halves of the wall together |
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How were openings supported in solid walls? |
With arches which usually had timber beams or lintels behind the face work to support the load. |
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Where should DPC be situated? |
Just above external ground level |
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Name a material used in early DPC |
Tar |
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What is the maximum U value of external walls |
0.35 |
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When were cavity walls introduced? |
1920's |
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What is the thickness of the cavity in a cavity wall? |
50-70mm |
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Name two functions of a cavity in a cavity wall? |
Prevent water from reaching the internal leaf Improves thermal efficiency as the air in the cavity is a good insulator. |
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Why are wall ties used? |
Because two independent walls are not very strong or stable |
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How often are wall ties placed> |
900mm apart every sixth course of bricks |
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What are washers used for |
Holding the cavity insulation in place |
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What is the minimum thickness requirement for party walls |
215mm solid wall or 250mm cavity wall |
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What is the minimum fire resistance time an external wall must meet? |
0.5 hours |
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What its the minimum fire resistance time a party wall must meet? |
1 hour |
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Why should DPC not cross the cavity? |
Because this would provide a path for water to run to the internal leaf. |
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Why is insulation fitted underneath the soffit |
To prevent condensation and hence dampq |
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In the earliest times why were buildings rendered with plaster? |
To make the windproof and weather tight |
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Name some of the qualities of plasterwork |
asy to clean, did not harbour dirt, was comfortable to the touch, and pleasing to the eye.retarded the spread of fire, especially on buildings of timber and helped deaden sound |
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How thick are Gypsum plasters |
13mm |
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What are the advantages of plaster boards |
Reduce time and delays ready to be self finished
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When is Gypsum plaster not suitable? |
On old walls as some contain chemicals which would harm the plaster. |
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Why the Gypsum plaster the most common type of plaster used? |
easy to use little risk of shrinkage cracking, set and dry quickly number of grades to suit most types of background. |
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What is the difference between old and new Gypsum plasters? |
Sand is not required |
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How should a background be prepared for plastering? |
Dry and protected from weather. |
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Name one problem that occurs when plastering composite walls |
Cracking occurs due to differential movement |
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What is the average thickness of an undercoat plastering layer? |
11mm |
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What is a the typical thickness of a finished plastering layer? |
2mm |
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What is the range of thicknesses for wallboards? |
9.5-19mm |
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What does dry lining mean? |
When plasterboard is used as a wall finish instead of wet plaster. |
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Why do plasterboards need to be mechanically fixed? |
To provide the required fire protection time. |
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What is the minimum contact area of a dab? |
20% of the board |
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When are noggins required? |
when joist centres are greater than 450mm |
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Nowadays where are load bearing partitions found? |
Usually one on the ground floor, unless the house is small, in this is may not contain any load bearing partitions. |
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In modern construction why are load bearing wall unnecessary on first floors? |
Because the roof structure is made of trussed rafters which only need support from external walls. |
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In portioning walls, how far apart are the stud centres placed? |
400mm |
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What is the purpose of noggins in partitioning walls? |
Noggings are used to stiffen up the partitioning |
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When should noggins be used? |
The the partitions are parallel to the joists |
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What is the typical size for timber used in a load bearing partitioning wall? |
100x50mm |
